Monday, 13 July 2009

Two Degrees

During last week's Group of 8 summit in L'Aquilla, Italy, leaders from the largest greenhouse gas emitting nations met to set the stage for December's climate change conference in Copenhagen. Together these 17 countries are responsible for 80% of global CO2 emissions.

Meetings like this are useful because they allow governments to broadcast their negotiating positions and begin edging towards compromise positions.

There's a lot that didn't happen during this meeting. China's president left early, the developing nations refused to commit to a reduction target, and while the industrialised nations agreed to reduce emissions 80% by the year 2050, they failed to state the base year - so we are left asking, "80% of what, precisely?".

And yet, there was a ray of hope. The G8 communique contained the following interesting passage:

"We reaffirm the importance of the work of the Intergovernmental Panel on Climate Change (IPCC) and notably of its Fourth Assessment Report, which constitutes the most comprehensive assessment of the science. We recognise the broad scientific view that the increase in global average temperature above pre-industrial levels ought not to exceed 2°C."

I believe this is the first time that a communique from heads of state has mentioned a temperature target. Most discussions to date have focused on emission levels, but I have always found this to be a bit abstract. Emissions affect the concentration of greenhouse gases in the atmosphere. Greenhouse gas concentrations affect the temperature, and the temperature change leads to the climactic changes about which we are all concerned.

Emissions levels are important, but they are hard to understand - they can't be seen or touched directly.

Temperature is another matter - a warming world can be felt by both people and ecosystems. So these world leaders have jumped two steps up the chain to talk about tangible outcomes - limiting temperature rises to two degrees Centigrade (about 3.6 degrees Fahrenheit).

Two degrees is about the maximum temperature that scientists think we can bear without reaching a "tipping point" into unpredictable and potentially catastrophic climate change impacts. Beyond that point, and we may enter a system where warming triggers feedback effects like methane releases from the sub-arctic tundra, CO2 releases forest die-offs, and less heat reflected back out to space due to melting glaciers.

Focusing on outcomes instead of processes gives us more flexibility to look at a range of options. It sets an ultimate test for any measure or negotiating position that is proposed in the run-up to Copenhagen: how effective

is this measure in keeping warming within two degrees?

So much for the good news. The bad news is that it's almost too late.

Alan Meyer of the Union of Concerned Scientists says that we've already warmed the planet by 0.8 degree, and time lags from the greenhouse gases already released mean that temperatures would rise another 0.6 degree even with no further pollution. So we have set a target to limit increases to 2 degrees, and we're already at 1.4.